1. Field of the Invention
The present invention relates to an optical disc cartridge, particularly, to improvements of openings for magnetic head and of a shutter.
2. Description of the Prior Art
FIG. 1 is a perspective view showing a construction of a conventional optical disc cartridge, and FIG. 2 is a sectional view of the above cut off through II--II line shown in FIG. 1. In FIG. 1, reference numeral 1 indicates a plastic case of an optical disc cartridge wherein a magneto optical disc 3 is housed. The case 1 is shaped like a flat board being hollow inside with a thickness of several mm, comprised of two flat members, that is, upper case 15 and lower case 16. At the lower case 16, a first opening including a rectangular hole 6 and a center hole 8 is formed. The first opening 4 is for an optical head (not shown) to access, and the width and length thereof are those which are enough for the optical head to access the magneto optical disc 3. Also, at the upper case 15, a second opening 5 of the same shape as that of the first opening is formed. The second opening 5 is for a magnetic head 10 to access, and the width and length thereof are those which are enough for the magnetic head 10 set up on an arm 9 shown in FIG. 2 to access the magneto optical disc 3. And, the upper case 15 has a thickness of l.sub.1.
A shutter 2 of stainless steel thin board, which closes both the openings 4 and 5 of the case 1 when an optical disc cartridge is taken out of the disc driving unit, is set up at one end of the case 1 so that it, having a section of U shape, has both faces of the case therebetween. The shutter 2 is installed so that it moved freely between a position for closing both openings 4 and 5 and a position for opening them. It is usually energized at the position for closing by means of a spring 11 (refer to FIG. 3). An aperture 7, facing the first opening 4 of the case 1 when the shutter 2 is at the position for opening and being the same shape as the first opening, is formed at the shutter 2, the magnetic head 10 accessing the magneto optical disc 3 therefrom. FIG. 3 through FIG. 6 show the case and the shutter in detail used in the case described above. FIG. 3 shows a plan view of the upper case 15 side of the optical disc cartridge, when the shutter 2 is at the position for closing. In the figure, reference numeral 11 is a spring which changes its shape by the movement of the shutter 2, and energizes the shutter 2 at the position for closing the opening 5. FIG. 4 shows a plan view of the lower case 16 side of the case 1. In the case of an optical disc cartridge, FIG. 4 shows the side of an optical head. In the figure, numeral 6 indicates a rectangular aperture used when an optical head (not shown) is inserted, and 8 indicates a circle aperture joining with the rectangular aperture, used for inserting a mount for fitting a magneto optical disc when the magneto optical disc is driven by a motor (not shown). These two apertures form a first opening 4. FIG. 5(a) is an enlarged view of the E portion in FIG. 4, and FIG. 5(b) is a plan view in the case where the FIG. 5(a) is taken as a front view and FIG. 5(c) is a sectional view when cut off through the K--K line shown in FIG. 5(b). In these figures, numeral 25 indicates an outside board of the lower case 16, and since a notch 16b is formed at an end side of the aperture 6 of the first opening 4, the outside board 25 is thinner by a predetermined length than the other part 24 of the lower case 16. This leads an optical head to smooth accessing. FIG. 6(a) is a plan view showing a conventional shutter, FIG. 6(b) is a left side view of the above, and FIG. 6(c) is a sectional view of the above cut off through the M--M line shown in FIG. 6(a). The under face 33 of the lower case 16 side of the shutter 2 is narrower in width in comparison with the top face 34 of the upper case 15 side, an aperture 7 of approximately the same shape as the second opening 5 of the upper case being formed at the top face 34. At the under face side of connecting portion 27 of the top face 34 with the under face 33, a notch 18 is formed having a width being the same as that of the aperture 7 and a depth corresponding to the notch 16b of the outside board 25 of the lower case 16.
Generally, a magnetic head is used for generating a biased magnetic field for overwriting. Since the magnitude of the magnetic field which is generated by a slider type magnetic head is small, it cannot be kept away from a recording medium as an optical head is. So, slider-type magnetic head 10 impresses a magnetic field in the state that it rises several through ten-odd .mu.m above a recording medium by means of dynamic pressure. (Fixed-type magnetic head is used in the state that it is kept about tens through 100 .mu.m apart from a recording medium.) Accordingly, in the conventional magneto optical disc, since the opening 5 is formed only on one side surface of the case, when an optical disc cartridge for a magneto optical disc is inserted into the disc driving unit, the magnetic head 10 needs to get over the end surface of the case 1, therefore causing a problem that the elevating mechanism has to be set up on an arm 9. This leads to a large-sized disc driving unit and complicated driving system of magnetic head.
Since the distance between the magnetic head 10 and the recording medium is very close, there is a problem that, in the case where the air inflowing from outside of the optical disc cartridge includes dust, the dust results in cutting off the air flow, thereby prohibiting the magnetic head 10 from rising and sometimes causing the magnetic head to fall down on the recording medium. Also, there is a problem that air flow is not stabilized on the surface of the recording medium which faces the magnetic head 10, since there is no air intake in the upper case 15.